In biology, taxonomy (from Ancient Greek τάξις (taxis) 'arrangement', and -νομία (-nomia) 'method') is the scientific study of naming, defining (circumscribing) and classifying groups of biological organisms based on shared characteristics. Organisms are grouped into taxa (singular: taxon) and these groups are given a taxonomic rank; groups of a given rank can be aggregated to form a more inclusive group of higher rank, thus creating a taxonomic hierarchy. The principal ranks in modern use are domain, kingdom, phylum (division is sometimes used in botany in place of phylum), class, order, family, genus, and species. The Swedish botanist Carl Linnaeus is regarded as the founder of the current system of taxonomy, as he developed a ranked system known as Linnaean taxonomy for categorizing organisms and binomial nomenclature for naming organisms.
With advances in the theory, data and analytical technology of biological systematics, the Linnaean system has transformed into a system of modern biological classification intended to reflect the evolutionary relationships among organisms, both living and extinct.
Definition
The exact definition of taxonomy varies from source to source, but the core of the discipline remains: the conception, naming, and classification of groups of organisms.[1] As points of reference, recent definitions of taxonomy are presented below:
Theory and practice of grouping individuals into species, arranging species into larger groups, and giving those groups names, thus producing a classification.[2]
A field of science (and a major component of systematics) that encompasses description, identification, nomenclature, and classification[3]
The science of classification, in biology the arrangement of organisms into a classification[4]
"The science of classification as applied to living organisms, including the study of means of formation of species, etc."[5]
"The analysis of an organism's characteristics for the purpose of classification"[6]
"Systematics studies phylogeny to provide a pattern that can be translated into the classification and names of the more inclusive field of taxonomy" (listed as a desirable but unusual definition)[7]
The varied definitions either place taxonomy as a sub-area of systematics (definition 2), invert that relationship (definition 6), or appear to consider the two terms synonymous. There is some disagreement as to whether biological nomenclature is considered a part of taxonomy (definitions 1 and 2), or a part of systematics outside taxonomy.[8][9] For example, definition 6 is paired with the following definition of systematics that places nomenclature outside taxonomy:[6]
Systematics: "The study of the identification, taxonomy, and nomenclature of organisms, including the classification of living things with regard to their natural relationships and the study of variation and the evolution of taxa".
In 1970, Michener et al. defined "systematic biology" and "taxonomy" (terms that are often confused and used interchangeably) in relation to one another as follows:[10]
Systematic biology (hereafter called simply systematics) is the field that (a) provides scientific names for organisms, (b) describes them, (c) preserves collections of them, (d) provides classifications for the organisms, keys for their identification, and data on their distributions, (e) investigates their evolutionary histories, and (f) considers their environmental adaptations. This is a field with a long history that in recent years has experienced a notable renaissance, principally with respect to theoretical content. Part of the theoretical material has to do with evolutionary areas (topics e and f above), the rest relates especially to the problem of classification. Taxonomy is that part of Systematics concerned with topics (a) to (d) above.
A whole set of terms including taxonomy, systematic biology, systematics, scientific classification, biological classification, and phylogenetics have at times had overlapping meanings – sometimes the same, sometimes slightly different, but always related and intersecting.[1][11] The broadest meaning of "taxonomy" is used here. The term itself was introduced in 1813 by de Candolle, in his Théorie élémentaire de la botanique.[12] John Lindley provided an early definition of systematics in 1830, although he wrote of "systematic botany" rather than using the term "systematics".[13] Europeans tend to use the terms "systematics" and "biosystematics" for the study of biodiversity as a whole, whereas North Americans tend to use "taxonomy" more frequently.[14] However, taxonomy, and in particular alpha taxonomy, is more specifically the identification, description, and naming (i.e., nomenclature) of organisms,[15] while "classification" focuses on placing organisms within hierarchical groups that show their relationships to other organisms.
Monograph and taxonomic revision
A taxonomic revision or taxonomic review is a novel analysis of the variation patterns in a particular taxon. This analysis may be executed on the basis of any combination of the various available kinds of characters, such as morphological, anatomical, palynological, biochemical and genetic. A monograph or complete revision is a revision that is comprehensive for a taxon for the information given at a particular time, and for the entire world. Other (partial) revisions may be restricted in the sense that they may only use some of the available character sets or have a limited spatial scope. A revision results in a conformation of or new insights in the relationships between the subtaxa within the taxon under study, which may lead to a change in the classification of these subtaxa, the identification of new subtaxa, or the merger of previous subtaxa.[16]
Taxonomic characters
Taxonomic characters are the taxonomic attributes that can be used to provide the evidence from which relationships (the phylogeny) between taxa are inferred.[17][18] Kinds of taxonomic characters include:[19]